Protective sensation, or ability to feel pain, is a warning system that enables an individual to avoid injury and that alerts the individual when injury does occur. Certain neurological and other medical examinations require the detection of impaired or lost sensitivity. Such detection is particularly important for patients with certain diseases or disabilities. For example, nearly half of all diabetes patients in the United States develop diabetic neuropathy, a complication that suppresses a patient's ability to feel pain. Diabetic peripheral neuropathy is characterized by loss of protective sensation, which may be manifested as analgesia (absence of pain or touch sensitivity), hyposthesia (reduced sensitivity), weakness, or autonomic changes. Loss of protective sensation is that degree of sensory loss that permits cutaneous injury to occur without being perceived by the patient as painful.
When due to neuropathy, loss of protective sensation is a major permissive factor in the pathogenesis of foot injury, and often leads to ulceration, infection, and, potentially, amputation. These problems are significant: Approximately 15% of diabetes patients sustain foot or leg ulcers, and may reacquire them in the absence of preventive and protective intervention. In addition, diabetic foot ulcers account for more than 20% of total hospital days for patients with diabetes, and they are the leading cause of hospital admissions for diabetic patients. Approximately 50% of all nontraumatic amputations in the United States are caused by complications from diabetes.
Routine testing for loss of protective sensation is critical, particularly for atrisk patients, such as those with diabetes. Prior art devices, however, are cumbersome and relatively expensive, and thus hinder such routine testing. For example, the device disclosed by Low et. al, U.S. Pat. No. 3,662,744, issued May 16, 1972, telescopically extends and retracts a monofilament. This device requires the health care practitioner to turn a knob to extend the monofilament each time the device is used, to ensure the proper length of monofilament is extended from the device, and to turn the knob to retract the monofilament when done. Because the length of monofilament extended from the device is variable, the health care practitioner has difficulty knowing how much force is being exerted by the monofilament on the patient. The device also has many moving parts, and thus is relatively costly to manufacture.
The Semmes-Weinstein esthesiometer, which currently is in widespread use, also has disadvantages. The Semmes-Weinstein device consists of a monofilament that is permanently attached at a 90 degree angle to the end of a plastic rod. The monofilament is always exposed, and thus is prone to damage. To compensate, the device generally is kept in a protective case in a drawer. The result is that the device is often not conveniently accessible to the health care provider, and thus is not used on a consistent basis.
There is an unmet need for a device for evaluating protective sensation that is convenient to carry and easy to operate and clean, thereby enabling health care practitioners to evaluate routinely whether their patents have lost protective sensation. Such a device preferably also will be inexpensive, small, and lightweight.